Commercial trucking provides a substantial proportion of commercial transportation of goods throughout the world. One common type of commercial truck is a tractor-trailer, which includes a semi-trailer coupled with a road tractor. The term “semi-trailer” typically refers to a trailer having one or more rear axles and no front axles. During operation, a large proportion of the weight of the semi-trailer is supported either by the road tractor or by a detachable front axle assembly known as a dolly. Semi-trailers are also normally equipped with legs that can be lowered to support the semi-trailer when it is uncoupled from the dolly or the road tractor.
As used herein, the term, “commercial motor vehicle” refers to any self-propelled or towed motor vehicle for use on a highway in interstate commerce to transport passengers or property and having a gross vehicle weight rating of 4,536 kilograms (approximately 10,000 pounds) or more. As used herein, the term, “gross vehicle weight rating” is the maximum allowable weight of a fully equipped tow vehicle including passengers and cargo. As used herein, the term, “Class A commercial motor vehicle” refers to any commercial vehicle having a gross vehicle weight rating (“GVWR”) of at least 11,793 kilograms (approximately 26,000 pounds).
Currently, in the United States, semi-truck trailers are typically on the order of 40 to 53 feet long and have a rear swing-open door providing an opening of about 110 inches high and 100 inches wide. Trucking operators seek to maximize the utilization of interior space within the trailer. Forklift trucks are typically used to load cargo into trailers. Specifically, cargo is supported by a pallet, which is lifted vertically by the forklift truck and deposited in the trailer. It is common for the forklift truck or other loading machine to push cargo from the rear open door of the trailer toward the front.
The typical trailer construction utilizes a roof of sheet metal or other opaque sheet material supported by a number of transversely extending reinforcing ribs or bows. These bows are exposed to the inside of the trailer and form irregularities on the inside surface of the trailer roof. During the loading process, it is unfortunately common for cargo or the cargo loading system to come in contact with one of the bows, potentially causing damage to the roof structure. Due to fear of damaging trailers in this manner, operators are often not able to fully utilize the interior capacity of the trailer. Damage to internal exposed roof bows during the cargo loading and unloading process imposes a significant operating cost burden on motor carrier operators and can cause shipping delays.
Furthermore, the opaque nature of currently-known trailer roofs causes the cargo space within the trailer to be generally void of natural light. Therefore, artificial light typically must be provided during loading and unloading of the cargo space.
A recent improvement in trailer construction is the development of trailer roofs with external bows. Such a design is described by U.S. Pat. No. 7,478,865. A trailer having a roof assembly constructed in accordance with that patent features a smooth inside roof surface. This is achieved by using transversely extending reinforcing bows which are mounted on the exterior or upper surface of the roof. The bow preferably have an inverted “U” or “W” shaped cross sectional configuration with flanges which engage the upper surface of the roof panel. External bows are used to support the roof panel using adhesives. This construction provides a smooth interior surface in the trailer which substantially reduces the likelihood of objects, containers, or machines becoming snagged on the roof bows.
For such trailers, a preferred material for the roof panel is a translucent composite material such as a fiberglass or other polymer material. By utilizing a translucent material, ambient light can reach the inside of the trailer which is convenient for trailer loading and unloading operations.
In order to provide a seamless roof panel structure to prevent water leakage, it is preferred that the external transversely extending roof bows are bonded to the roof using adhesive materials or tapes. In the production process, it is preferred that the roof panel is held in position to the side, front, and rear panels of the trailer through the use of frame rails which sandwich the roof panel between the frame rail and the existing perimeter structural members of the trailer. Rivets or other mechanical fasteners can be used to support the perimeter of the roof panel. Thereafter, the externally mounted roof rails are mounted on top of the roof panel with its ends riveted or otherwise mechanically attached to the side rail structure.
Assembly of the roof of the above-described design is achieved using a fixture which supports the roof panel in a convex crowned shape, enabling the external roof bows to be bonded to the roof panel.
The design provided by the previously mentioned issued patent provides outstanding performance benefits and that design is being widely adopted. However, there is a continuing need to improve the design of these systems. In particular, the external bows of the previously mentioned patent are formed from sheet metal stock. Although forming sheet metal is generally an inexpensive fabrication process, formed sheet metal bows may not provide an ideal surface for providing bonding agents for attachment of the roof panel to the bows. Moreover, the manufacturing process of forming sheet metal into the bows limits the freedom of design of the bow configuration. In particular, in cross-section, a sheet metal formed bow has a generally uniform material thickness and the degrees of bending and other forming limitations are present.
In accordance with the present invention, an improved roof bow is provided for external bow semi-trailer applications.